The invention relates to a centered double joint with two universal joints each consisting of an inner yoke and an outer yoke and a cross member which connects the two and which, via bearings, is held in bores of the yokes. The two inner yokes are connected to each other and the two outer yokes, via engaging centering devices centrically attached to a bridge connecting their yoke arms, are guided either directly relative to each other or by inserting a guiding disc radially movable between the inner yokes. One of the centering devices being a sleeve and the other one a spherical journal guided therein, and the centering device associated with the bridge having a lubricating channel which for lubricating purposes is connected to the lubricating channels of the cross member.
With such an assembly, known from DE 31 42 930 C2, the cross member is associated with a slidable piston which for lubricating purposes has to be moved into a congruent position relative to the lubricating channel in the centering device and which establishes contact as a result of the pressure of the lubricant. A further embodiment proposes a lubricating position at maximum articulation, with the lubricating channels in the centering device and in the cross member having to be moved into congruent positions.
From DE 31 38 190 C2 is it known to provide the cross member with a central spherical recess into which an insert with a partially spherical outer face is inserted, with the other end of the insert closely resting against and being supported on the bridge comprising a lubricating channel.
With the first prior art solution, to effect lubrication, it is necessary to first find the right lubricating position to prevent the lubricant pressed into the cross member from escaping without reaching the lubricating regions of the centering device to be lubricated. With the second embodiment there exists a permanent connection, but in the region of the cross member a considerable amount of machining is necessary for providing the ball socket for the insert. The same applies to the supporting face on which the insert is supported on the bridge. Furthermore, to accommodate the ball socket, the cross member has to be weakened in its center.